1. Field of the Invention
The present invention relates to patient monitoring. Although embodiments make specific reference to monitoring impedance and electrocardiogram signals with an adherent patch, the system methods and device described herein may be applicable to many applications in which physiological monitoring is used, for example wireless physiological monitoring for extended periods.
Patients are often treated for diseases and/or conditions associated with a compromised status of the patient, for example a compromised physiologic status. In some instances, a patient may report symptoms that require diagnosis to determine the underlying cause. For example, a patient may report fainting or dizziness that requires diagnosis, in which long term monitoring of the patient can provide useful information as to the physiologic status of the patient. In some instances a patient may have suffered a heart attack and require care and/or monitoring after release from the hospital. One example of a device to provide long term monitoring of a patient is the Holter monitor, or ambulatory electrocardiography device.
In addition to measuring heart signals with electrocardiograms, known physiologic measurements include impedance measurements. For example, transthoracic impedance measurements can be used to measure hydration and respiration.
Work in relation to embodiments of the present invention suggests that known methods and apparatus for long term monitoring of patients may be less than ideal. Although transthoracic measurements can be useful, such measurements may use electrodes that may be somewhat uncomfortable and/or cumbersome for the patient to wear. Also, it would be helpful to detect subtle changes in patient physiology, for example based on subtle changes in electrocardiogram signals and/or patient hydration signals. In at least some instances, electrodes that are held against the skin of the patient can become detached and/or dehydrated, such that the electrodes must be replaced. Replacement of electrodes can result in a change in the orientation of the electrodes that may affect the measured signal in at least some instances. Examples of physiological measurements that may be affected by electrode placement include electrocardiogram signals and tissue impedance signals to measure hydration and/or respiration of a patient. Therefore, a need exists to improve the quality of long term patient measurements with external devices, for example those worn by the patient.
Although implantable devices may be used in some instances, many of these devices can be invasive and/or costly, and may suffer at least some of the shortcomings of known wearable devices.
Therefore, a need exists for improved patient monitoring. Ideally, such improved patient monitoring would avoid at least some of the short-comings of the present methods and devices.
2. Description of the Background Art
The following US patents and Publications may describe relevant background art: U.S. Pat. Nos. 4,121,573; 4,478,223; 4,850,370; 4,955,381; 4,981,139; 5,080,099; 5,125,412; 5,331,966; 5,353,793; 5,511,553; 5,544,661; 5,558,638; 5,724,025; 5,772,586; 5,862,802; 5,970,986; 5,987,352; 6,047,203; 6,052,615; 6,117,077; 6,129,744; 6,225,901; 6,385,473; 6,416,471; 6,454,707; 6,480,733; 6,496,715; 6,527,711; 6,527,729; 6,551,252; 6,595,927; 6,595,929; 6,605,038; 6,611,705; 6,645,153; 6,699,200; 6,821,249; 6,912,414; 6,881,191; 6,980,851; 7,020,508; 7,054,679; 7,153,262; 7,206,630; 2002/0045836; 2003/0092975; 2003/0149349; 2005/0065445; 2005/0113703; 2005/0131288; 2005/0267381; 2006/0010090; 2006/0031102; 2006/0089679; 2006/0116592; 2006/0122474; 2006/0155183; 2006/0253044; 2006/0224051; 2006/0264730; 2007/0016089; 2007/0021678; 2007/0038038; 2007/0073132; 2007/0142715; 2007/0167849; 2007/0167850; and 2007/0208233.